LED lighting apparatus having improved color lendering and LED filament

ABSTRACT

A lighting apparatus including at least one light emitting diode (LED) chip configured to emit blue light; a green phosphor having a light emission peak in a range of 500 nm to 550 nm; and a red phosphor having a light emission peak in a range of 600 nm to 650 nm, in which the red phosphor includes a first red phosphor having a light emission peak in a range of 620 nm to 630 nm and a second red phosphor having a light emission peak in a range of 630 nm to 640 nm, and the full widths at half maximum of the first and second red phosphors are in a range of 20 nm to 60 nm, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Entry of International PatentApplication No. PCT/KR2019/001534, filed on Feb. 7, 2019, and claimspriority from and the benefit of Korean Patent Application No.10-2018-0022178, filed on Feb. 23, 2018, each of which is herebyincorporated by reference for all purposes as if fully set forth herein

BACKGROUND Field

Exemplary embodiments of the present disclosure relate to a lightingapparatus, and, more particularly, to an LED lighting apparatus and anLED filament having improved color rendering.

Discussion of the Background

Light bulbs typically generate light using metal filaments, such astungsten. However, light bulbs with metal filaments are quickly beingreplaced by LED lamps because conventional light bulbs have shorterlifespan, lower light efficiency, and higher power consumption than LEDlamps.

An LED lighting apparatus, such as an LED lamp, generally uses LEDs thatemit light in the blue region as a light source. In particular, the LEDlighting apparatus that implements white light uses a phosphor alongwith the LEDs.

High color rendering is generally required for lighting apparatuses thatimplement white light. Color rendering is an illumination property of alight source that indicates how similar an object color irradiated bythe lighting apparatus is to an object color irradiated by a referencelight source. The color rendering is evaluated by the color renderingindex (CRI), and a general color rendering index (Ra) is widely used. Rais the average value of the individual color rendering indices (specialCRIs; R1 to R8) quantified using eight test color samples.

In general, when Ra exhibits a high value, the color rendering of theillumination light source is considered high. However, increasing Ra ina lighting apparatus using a blue LED as the light source generallyleads to a decrease in the luminous intensity, thereby increasing powerconsumption. Furthermore, since Ra is the average value of individualcolor rendering indices, high Ra does not necessarily mean that R1 to R8are all evenly high. In particular, since the LED lighting apparatususing the blue LED lacks light in the red region, the value of R8measured using a test color sample having a high reflectance in the pinkregion is generally relatively low compared to R1 to R7. Therefore,there is a need for an LED lighting apparatus capable of increasing R8while achieving appropriate Ra.

While the phosphor in the red region may be added to sufficientlyincrease the value of R8, in this case, unnecessary light may begenerated due to a considerable amount of tail generated in the emissionspectrum of the red phosphor, thereby deteriorating the efficiency ofthe lighting apparatus. A mainly used nitride-based red phosphor, suchas CaAlSiN₃:Eu²⁺, has a full width at half maximum of about 80 nm ormore, and when a nitride phosphor having an emission peak of about 650nm is used, a considerable amount of light is generated even in a regionof 700 nm or more. Accordingly, when the amount of red phosphor isincreased to increase R8, Ra is increased as a whole and the overallluminous intensity of the lighting apparatus is lowered. That is, it isdifficult to increase R8 without reducing the luminous intensity of thelighting apparatus with the nitride-based red phosphor. In addition,although the luminous intensity may be increased by increasing thenumber of lighting apparatuses or increasing the number of LEDs and anamount of phosphors in the lighting apparatus, such would undesirablyincrease power consumption.

Recently, K₂SiF₆:Mn⁴⁺(KSF) has been used as the red phosphor having anarrow full width at half maximum. The KSF phosphor has a very narrowfull width at half maximum of less than about 10 nm, and, accordingly,is a phosphor capable of implementing good color reproducibility. Whenusing the red phosphor having the narrow full width at half maximum,such as KSF, it is possible to remove unnecessary tails and emit lightin the desired red region, thereby achieving high R8 even withrelatively low Ra. That is, appropriate Ra and R8 may be achievedwithout significantly reducing the luminous intensity. However, sincethe full width at half maximum is narrow, there is a problem that anamount of the KSF phosphor used is more considerably increased than whenthe nitride-based red phosphor is used. In general, when the KSFphosphor is used, the amount of phosphor used may be increased by sixtimes or more than when using the nitride-based phosphor, thus,increasing R8 by using KSF may not be a proper choice. In addition, theKSF phosphor is relatively expensive compared to other red phosphors,and is difficult to purchase as a phosphor, and thus, there are manyrestrictions in using the KSF.

SUMMARY

Exemplary embodiments provide a LED lighting apparatus capable ofimproving R8 while preventing the reduction of the luminous intensity ofthe lighting apparatus.

Exemplary embodiments also provide an LED lighting apparatus capable ofincreasing R8 without increasing an amount of phosphor used.

Additional features of the inventive concepts will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the inventive concepts.

A lighting apparatus according to an exemplary embodiment includes: alight emitting diode chip emitting blue light; a green phosphor havingan emission peak in a range of 500 nm to 550 nm; and a red phosphorhaving an emission peak in a range of 600 nm to 650 nm, in which the redphosphor includes: a first red phosphor having an emission peak in arange of 620 nm to 630 nm; and a second red phosphor having an emissionpeak in a range of 630 nm to 640 nm, in which full widths at halfmaximum of the first red phosphor and the second red phosphor are in arange of 20 nm to 60 nm, respectively.

A general color rendering index (Ra) of the lighting apparatus may be ina range of 80 to 98, and an R8 thereof may be greater than 72.

The first red phosphor and the second red phosphor may include (Ca,Sr)S:Eu-based phosphors. However, the inventive concepts are not limitedto a specific sulfide phosphor, and other red phosphors whose emissionpeak and full width at half maximum satisfy the above conditions may beused.

Full widths at half maximum of the first red phosphor and the second redphosphor may be in a range of 50 nm to 60 nm.

The green phosphor may include a Lu₃(Al, Ga)₅O₁₂:Ce (LuAG)-basedphosphor.

The lighting apparatus may further include a yellow phosphor having anemission peak in a range of 550 nm to 600 nm.

A mixing ratio of the green phosphor, the yellow phosphor, and the redphosphor may be adjusted to obtain a desired color rendering index. Inaddition, since two kinds of red phosphors having a relatively narrowfull width at half maximum are used, desired R8 may be achieved withoutreducing the luminous intensity.

The lighting apparatus may include an LED filament. The LED filament mayinclude: a supporting substrate on which the LED chips are disposed;wires electrically connecting the LED chips; and an encapsulant coveringthe LED chips, in which the green phosphor and red phosphor may bedistributed in the encapsulant. Further, the encapsulant may surroundthe supporting substrate.

An LED filament according to another exemplary embodiment may include: asupporting substrate; a plurality of light emitting diode chips disposedon the supporting substrate, and emitting blue light; and an encapsulantcovering the plurality of light emitting diode chips and havingphosphors distributed therein, in which the phosphors may include: agreen phosphor having an emission peak in a range of 500 nm to 550 nm;and a red phosphor having an emission peak in a range of 600 nm to 650nm, in which the red phosphor may include: a first red phosphor havingan emission peak in a range of 620 nm to 630 nm; and a second redphosphor having an emission peak in a range of 630 nm to 640 nm, inwhich full widths at half maximum of the first red phosphor and thesecond red phosphor are in a range of 20 nm to 60 nm, respectively.

Ra of the LED filament ray be in a range of 80 to 98, and R8 may begreater than 72.

The first red phosphor and the second red phosphor may include (Ca,Sr)S:Eu-based phosphors.

Full widths at half maximum of the first red phosphor and the second redphosphor may be in a range of 50 nm to 60 nm.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theinventive concepts.

FIG. 1 is a schematic front view illustrating an LED lamp according toan exemplary embodiment.

FIG. 2 is a schematic plan view illustrating an LED filament accordingto an exemplary embodiment.

FIGS. 3A and 3B show partially enlarged cross-sectional views of an LEDfilament according to exemplary embodiments.

FIG. 4 is a schematic plan view of a light emitting diode chip mountedon an LED filament according to an exemplary embodiment.

FIG. 5 is a cross-sectional view taken along the line A-A of FIG. 4 .

FIG. 6 is a graph showing luminous fluxes and R8s of lightingapparatuses according to comparative examples and an exemplaryembodiment.

FIG. 7 is a graph showing amounts of phosphors used in lightingapparatuses.

FIG. 8A and FIG. 8B are graphs showing emission spectra of a comparativeexample and an exemplary embodiment.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments or implementations of theinvention. As used herein “embodiments” and “implementations” areinterchangeable words that are non-limiting examples of devices ormethods employing one or more of the inventive concepts disclosedherein. It is apparent, however, that various exemplary embodiments maybe practiced without these specific details or with one or moreequivalent arrangements. In other instances, well-known structures anddevices are shown in block diagram form in order to avoid unnecessarilyobscuring various exemplary embodiments. Further, various exemplaryembodiments may be different, but do not have to be exclusive. Forexample, specific shapes, configurations, and characteristics of anexemplary embodiment may be used or implemented in another exemplaryembodiment without departing from the inventive concepts.

Unless otherwise specified, the illustrated exemplary embodiments are tobe understood as providing exemplary features of varying detail of someways in which the inventive concepts may be implemented in practice.Therefore, unless otherwise specified, the features, components,modules, layers, films, panels, regions, and/or aspects, etc.(hereinafter individually or collectively referred to as “elements”), ofthe various embodiments may be otherwise combined, separated,interchanged, and/or rearranged without departing from the inventiveconcepts.

The use of cross-hatching and/or shading in the accompanying drawings isgenerally provided to clarify boundaries between adjacent elements. Assuch, neither the presence nor the absence of cross-hatching or shadingconveys or indicates any preference or requirement for particularmaterials, material properties, dimensions, proportions, commonalitiesbetween illustrated elements, and/or any other characteristic,attribute, property, etc., of the elements, unless specified. Further,in the accompanying drawings, the size and relative sizes of elementsmay be exaggerated for clarity and/or descriptive purposes. When anexemplary embodiment may be implemented differently, a specific processorder may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order. Also, like reference numerals denote like elements.

When an element, such as a layer, is referred to as being “on,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, connected to, or coupled to the other element or layer orintervening elements or layers may be present. When, however, an elementor layer is referred to as being “directly on,” “directly connected to,”or “directly coupled to” another element or layer, there are nointervening elements or layers present. To this end, the term“connected” may refer to physical, electrical, and/or fluid connection,with or without intervening elements. Further, the D1-axis, the D2-axis,and the D3-axis are not limited to three axes of a rectangularcoordinate system, such as the x, y, and z-axes, and may be interpretedin a broader sense. For example, the D1-axis, the D2-axis, and theD3-axis may be perpendicular to one another, or may represent differentdirections that are not perpendicular to one another. For the purposesof this disclosure, “at least one of X, Y, and Z” and “at least oneselected from the group consisting of X, Y, and Z” may be construed as Xonly, Y only, Z only, or any combination of two or more of X, Y, and Z,such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Although the terms “first,” “second,” etc. may be used herein todescribe various types of elements, these elements should not be limitedby these terms. These terms are used to distinguish one element fromanother element. Thus, a first element discussed below could be termed asecond element without departing from the teachings of the disclosure.

Spatially relative terms, such as “beneath,” “below,” “under,” “lower,”“above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), andthe like, may be used herein for descriptive purposes, and, thereby, todescribe one elements relationship to another element(s) as illustratedin the drawings. Spatially relative terms are intended to encompassdifferent orientations of an apparatus in use, operation, and/ormanufacture in addition to the orientation depicted in the drawings. Forexample, if the apparatus in the drawings is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below.Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90degrees or at other orientations), and, as such, the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof. It is also noted that, as used herein, the terms“substantially,” “about,” and other similar terms, are used as terms ofapproximation and not as terms of degree, and, as such, are utilized toaccount for inherent deviations in measured, calculated, and/or providedvalues that would be recognized by one of ordinary skill in the art.

Various exemplary embodiments are described herein with reference tosectional and/or exploded illustrations that are schematic illustrationsof idealized exemplary embodiments and/or intermediate structures. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary embodiments disclosed herein should notnecessarily be construed as limited to the particular illustrated shapesof regions, but are to include deviations in shapes that result from,for instance, manufacturing. In this manner, regions illustrated in thedrawings may be schematic in nature and the shapes of these regions maynot reflect actual shapes of regions of a device and, as such, are notnecessarily intended to be limiting.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and should not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

Hereinafter, an LED lighting apparatus will be described with referenceto an LED lamp. However, the inventive concepts are not limited thereto,and the LED lighting apparatus may be employed in various other types oflighting apparatuses.

FIG. 1 is a schematic front view illustrating an LED lamp according toan exemplary embodiment.

Referring to FIG. 1 , the LED lamp includes a bulb base 10, a centerpillar 20, a lower lead wire 30, an upper lead wire 40, an LED filament50, and a light transmissive bulb 60.

The bulb base 10 may have an electrode structure that may be used in aconventional light bulb. In addition, passive and active devices, suchas an AC/DC converter, may be built in the bulb base 10.

Since the bulb base 10 may have the same electrode structure as that ofthe conventional light bulb, the LED lamp according to an exemplaryembodiment may be used in a conventional socket. As such, installationcosts of additional facilities from using the LED lamp may be saved.

The center pillar 20 is fixed to the bulb base 10, and disposed at acenter of the LED lamp. The center pillar 20 may include a supporter, apillar, and an upper end. The center pillar 20 is for supporting the LEDfilaments 50, and, for example, may be formed of glass.

The lower lead wire 30 electrically connects the bulb base 10 and theLED filament 50. The lower lead wire 30 is coupled to a lower endportion of the LED filament 50. The lower lead wire 30 is connected toeach LED filament 50. More particularly, the lower lead wires 30 aredivided into two groups, and are connected to two electrodes of the bulbbase 10, respectively.

The upper lead wire 40 is coupled to an upper end portion of the LEDfilaments 50. A single upper lead wire 40 may connect a pair of LEDfilaments 50 to each other. In the illustrated exemplary embodiment, twopairs of LED filaments 50 are shown, with two upper lead wires 40connecting the two pairs of LED filaments 50 in series. However, theinventive concepts are not limited thereto, and in some exemplaryembodiments, a pair or three or more pairs of LED filaments 50 connectedto each other through the upper lead wire 40 may be disposed.

The light transmissive bulb 60 surrounds the LED filament 50, and isseparated from an external environment. The light transmissive bulb 60may be formed of glass or plastic. The light transmissive bulb 60 mayhave various shapes, and may have the same shape as the conventionalbulb.

The LED filament 50 is electrically connected to the bulb base 10through the lower lead wire 30 and the upper lead wire 40. A structureof the LED filament 50 will be described in detail with reference toFIG. 2 and FIG. 3 .

FIG. 2 is a schematic plan view illustrating an LED filament accordingto an exemplary embodiment, and FIGS. 3A and 3B show partially enlargedcross-sectional views of an LED filament according to exemplaryembodiment.

Referring to FIG. 2 and FIGS. 3A and 3B, the LED filament 50 may includea supporting substrate 51, a light emitting diode chip 53, a bondingwire 54, an encapsulant 55, and first and second metal plates 56. Inaddition, an adhesive 52 for bonding the light emitting diode chip 53 tothe supporting substrate 51 may be disposed between the light emittingdiode chip 53 and the supporting substrate 51. In addition, the firstand second metal plates 56 may also be attached to the supportingsubstrate 51 using the adhesive.

The supporting substrate 51 has an elongated shape, such as a bar. Thesupporting substrate 51 may also have a first surface and a secondsurface opposite to the first surface. The supporting substrate 51 maybe formed of a transparent substance, such as sapphire, quartz, orglass, but is not limited thereto, and may be formed of various kinds oftransparent or opaque ceramics.

The LED chips 53 are disposed on the supporting substrate 51. The lightemitting diode chips 53 may be disposed on the first surface of thesupporting substrate 51, or may be disposed on both of the first surfaceand the second surface. The light emitting diode chips 53 may be bondedonto the supporting substrate 51 without an adhesive using a waferbonding technique, or may be bonded onto the supporting substrate 51using the adhesive 52. In an exemplary embodiment, a transparentadhesive is used for the adhesive 52, and, in another exemplaryembodiment, the adhesive 52 may include wavelength convertingsubstances, such as phosphors or quantum dots.

The bonding wires 54 electrically connect the LED chips 53. The LEDchips 53 may be connected in series through the bonding wires 54 asshown in the drawings. The upper lead wire 40 of FIG. 1 may connect apair of LED filaments 50 to each other in series. The LED chips 53disposed at both end portions of the supporting substrate 51 areelectrically connected to the first and second metal plates 56,respectively. These light emitting diode chips 53 may also beelectrically connected to the first and second metal plates 56 throughthe bonding wire 54.

The encapsulant 55 covers the light emitting diode chips 53, and alsocovers the bonding wires 54. The encapsulant 55 may also partially coverthe first and second metal plates 56. Although the encapsulant 55 maycover the LED chips 53 on the first surface of the supporting substrate51 as shown in FIG. 3A, according to another exemplary embodiment, theencapsulant 55 may be formed to surround all of the first and secondsurfaces of the supporting substrates as shown in FIG. 3B. Theencapsulant 55 may include phosphors converting wavelengths of lightemitted from the light emitting diode chips 53. The phosphors in theencapsulant 55 will be described in detail later.

The first and second metal plates 56 are coupled to the supportingsubstrate 51. The first and second metal plates 56 may be attached tothe supporting substrate 51 through an adhesive, but are not limitedthereto, and may be coupled to the supporting substrate 51 in variousways.

As described with reference to FIG. 1 , one end portion of the LEDfilament 50 is connected to the lower lead wire 30, and the other endportion is connected to the upper lead wire 40. In this case, the firstand second metal plates 56 may be coupled to the lower lead wire 30 andthe upper lead wire 40 by soldering, welding, or the like.

In addition, the lower lead wire 30 and the upper lead wire 40 may haveelasticity, and, accordingly, when the LED filament 40 expands orcontracts with heat, the lower and upper lead wires 30 and 40 may bent.

FIG. 4 is a schematic plan view of a light emitting diode chip 53mounted on an LED filament according to an exemplary embodiment, andFIG. 5 is a cross-sectional view taken along line A-A of FIG. 4 .

Referring to FIG. 4 and FIG. 5 , the light emitting diode chip 53 mayinclude a growth substrate 110, an n-side semiconductor layer 120, anactive layer 130, a p-side semiconductor layer 140, and a transparentelectrode 150, an n-electrode 160, and a p-electrode 170.

The growth substrate 110 is a substrate suitable for growing a galliumnitride-based semiconductor layer thereon, and may be a transparentsubstrate transmitting light generated in the active layer 130. Forexample, the growth substrate 110 may be a sapphire substrate, a galliumnitride substrate, an aluminum nitride substrate, or the like, and, inparticular, may be a patterned sapphire substrate. FIG. 5 exemplarilyshows the patterned sapphire substrate, in which protrusions 115 areformed on a upper surface of the substrate 110.

A semiconductor stacked structure including the n-side semiconductorlayer 120, the active layer 130, and the p-side semiconductor layer 140is disposed on the growth substrate 110.

The transparent electrode 150 may be disposed on the p-sidesemiconductor layer 140 and contact the p-side semiconductor layer 140.The transparent electrode 150 transmits light generated in the activelayer 130. The transparent electrode 150 may be formed of a transparentoxide film, such as indium-tin-oxide (ITO), ZnO, or the like, or atransparent metal, such as Ni/Au, or the like.

Portions of the p-side semiconductor layer 140 and the active layer 130may be removed to expose the n-side semiconductor layer 120. Then-electrode 160 is formed on the exposed n-side semiconductor layer 120,and electrically connected to the n-side semiconductor layer 120. Then-electrode 160 may be in ohmic contact with the n-side semiconductorlayer 120, and may be formed of, for example, Ti/Al.

The p-electrode 170 is formed on the transparent electrode 150. Aportion of the transparent electrode 150 may have an opening exposingthe p-side semiconductor layer 140, and the p-electrode 170 may contactthe p-side semiconductor layer 140 through the opening formed in thetransparent electrode 150. The p-electrode 170 may include a reflectivelayer for reflecting light incident from the active layer 130. Forexample, the p-electrode 170 may be formed of Al/Ti/Pt/Au.

An extension 175 may extend from the p-electrode 170 toward then-electrode 160. The extension 175 may and the p-electrode 170 may beformed together and may include substantially the same material.

The semiconductor stacked structure disposed on the growth substrate 110includes the n-side semiconductor layer 120, the active layer 130, andthe p-side semiconductor layer 140 as described above. The semiconductorstacked structure described herein may be formed of a galliumnitride-based semiconductor layer, and may be grown on the growthsubstrate 110 using a metal organic chemical vapor deposition method, ahydride vapor deposition method, or the like.

The n-side semiconductor layer 120 may have a single layer or amultilayer structure. For example, the n-side semiconductor layer 120may include a buffer layer and an n-type contact layer. The buffer layermay be formed of GaN, and may be formed to reduce crystal defects due tolattice mismatch between the growth substrate 110 and the semiconductorlayer.

The active layer 130 may have a single quantum well structure or amultiple quantum well structure. In particular, the active layer 130 mayhave a multiple quantum well structure in which a barrier layer and awell layer are alternately stacked, and thus, the internal quantumefficiency may be improved.

The p-side semiconductor layer 140 may have a single layer or amultilayer structure, and may include, for example, an electron blockinglayer and a p-type contact layer.

The electron blocking layer is disposed on the active layer 130, andconfines electrons in the active layer 130 to improve recombinationrate. The electron blocking layer may be formed of AlGaN or AlInGaN.

The p-type contact layer is a layer doped with a p-type impurity, suchas Mg, and the transparent electrode 150 is electrically connected tothe p-type contact layer.

Although the light emitting diode chip 53 according to one exemplaryembodiment has been described, the inventive concepts are not limited tothe illustrated light emitting diode chip, and various kinds of bluelight emitting diode chips may be used in other exemplary embodiments.

The light emitting diode chip 53 may have a light emission peak in theblue region, for example, in a range of 450 nm to 470 nm, and further ina range of 450 nm to 460 nm. Phosphors included in the encapsulant 55may convert light emitted from the light emitting diode chip 53.

In particular, the phosphor includes a green phosphor having an emissionpeak in a range of 500 nm to 550 nm and a red phosphor having anemission peak in a range of 600 nm to 650 nm. Further, in theillustrated exemplary embodiment, the red phosphor includes a first redphosphor having an emission peak in a range of 620 nm to 630 nm and asecond red phosphor having an emission peak in a range of 630 nm to 640nm. Full widths at half maximum of the first red phosphor and the secondred phosphor may be in a range of 20 nm to 60 nm, respectively, and maybe further, in a range of 40 nm to 60 nm, specifically, in a range of 50nm to 60 nm. The first and second red phosphors may be, for example,(Ca, Sr)S:Eu²⁺-based sulfide phosphors, without being limited thereto.

The red phosphor having the full width at half maximum of 20 nm to 60 nmmay improve R8 without reducing the luminous intensity of the lightingapparatus because a tail region of the unnecessary wavelength band issmall. Moreover, since the full width at half maximum is not extremelynarrow like that of the KSF phosphor, the amount of the phosphor used toimprove R8 according to an exemplary embodiment may not need to beincreased.

Furthermore, the first red phosphor having the emission peak in therange of 620 nm to 630 nm and the second red phosphor having theemission peak in the range of 630 nm to 640 nm are used together, andthus, a relatively large region of the red region for improving R8 maybe easily covered. Accordingly, it is possible to reduce the amount ofphosphor used for achieving an equivalent Ra as compared to using anitride-based phosphor.

The green phosphor has an emission peak in a range of 500 nm to 550 nm.The green phosphor is not particularly limited, but a Lu₃(Al, Ga)₅O₁₂:Ce(LuAG)-based phosphor, a silicate phosphor, such as Ba₂MgSi₂O₇:Eu²⁺,Ba₂SiO₄:Eu²⁺, Ca₃(Sc, Mg)₂Si₃O₁₂:Ce³⁺, or the like, or a sulfidephosphor, such as (Sr, Ca)Ga₂S₄:Eu²⁺, or the like may be used, forexample. In particular, the green phosphor may have a full width at halfmaximum in a range of 90 nm to 130 nm, thereby covering a relativelywide wavelength region.

The phosphor may further include a yellow phosphor. For example, a YAGphosphor or a silicate phosphor may be used. The yellow phosphor mayhave an emission peak in a range of 550 nm to 600 nm, and may have awide full width at half maximum of 100 nm or more, like the greenphosphor.

FIG. 6 is a graph showing luminous fluxes and R8 of lighting apparatusesaccording to comparative examples and an exemplary embodiment.

In the lighting apparatus of the comparative examples and that of theexemplary embodiment, LED chips of the same type were disposed on asupporting substrate, and the supporting substrate was covered with anencapsulant including a phosphor. In addition, except for a redphosphor, homologous LuAG-based phosphors and YAG phosphors were used.Meanwhile, for the comparative example, two kinds of nitride-basedphosphors were used as red phosphors, and two kinds (Ca, Sr)S:Eu²⁺sulfide phosphors were used as red phosphors for the exemplaryembodiment.

The nitride-based phosphors had emission peaks of about 635 nm and 646nm, and full widths at half maximum thereof were about 92.5 nm and 87.5nm, respectively. On the other hand, the sulfide phosphors had emissionpeaks of about 626 nm and 634 nm, and full widths at half maximumthereof were about 53.5 nm and about 56.5 nm, respectively.

A mixing ratio of these phosphors was adjusted to prepare ComparativeExample 1 having a Ra (CRI) of about 80 and Comparative Example 2 havinga Ra (CRI) of about 90, and Exemplary Embodiment 1 having a Ra of about80.

When the luminous flux of the lighting apparatus of Comparative Example1 having Ra of 80 was 100, the luminous flux of Comparative Example 2having Ra of 90 was reduced by 10% or more compared with ComparativeExample 1. In contrast, the luminous flux of the lighting apparatus ofExemplary Embodiment 1 having Ra of 80 was slightly reduced comparedwith Comparative Example 1.

Meanwhile, the lighting apparatus of Comparative Example 1 having Ra of80 had R8 of less than 60, and lighting apparatus of Comparative Example2 having Ra of 90 had R8 of 80 or more. Meanwhile, for the ExemplaryEmbodiment 1, Ra was 80 and R8 was 72 or more.

That is, according to Exemplary Embodiment 1, two kinds of red phosphorshaving relatively small full widths at half maximum were mixed to use,and thus, it was possible to increase R8 to 72 or more while keeping Rarelatively low. On the other hand, when using nitride-based phosphorshaving relatively large full widths at half maximum as in ComparativeExamples 1 and 2, it can be seen that Ra needs to be increased toachieve high R8, and thus, the luminous flux is considerably reduced.

FIG. 7 is a graph showing amounts of phosphors used in lightingapparatuses.

To achieve the same Ra 80, the amount of phosphors used in the lightingapparatus was compared. Comparative Example 1 and Exemplary Embodiment 1are the same as described above, and Comparative Example 3 uses a KSFphosphor as a red phosphor.

When the amount of the nitride phosphor was 100%, the KSF phosphor wasused more than six times, almost seven times, and an amount of thesulfide phosphor used was lower than that of the nitride phosphor.

FIG. 8A and FIG. 8B are graphs showing emission spectra of ComparativeExample 1 and Exemplary Embodiment 1.

As can be seen from FIG. 8A and FIG. 8B, when the red phosphor ofExemplary embodiment 1 having the narrow full width at half maximum isused, the luminous intensity of the red light wavelength region isimproved. Furthermore, since the phosphors having the narrow full widthsat half maximum are used, tails generated on a side of the longwavelength may be reduced, and thus, the luminous intensity may beincreased while improving R8.

According to exemplary embodiments, since two kinds of red phosphorshaving full widths at half maximum in a range of 20 nm to 60 nm areused, favorable color rendering with R8 of 72 or more may be achievedwithout increasing the amount of phosphors used, thereby preventing theluminous intensity of a lighting apparatus from being reduced.

Although certain exemplary embodiments and implementations have beendescribed herein, other embodiments and modifications will be apparentfrom this description. Accordingly, the inventive concepts are notlimited to such embodiments, but rather to the broader scope of theappended claims and various obvious modifications and equivalentarrangements as would be apparent to a person of ordinary skill in theart.

What is claimed is:
 1. A lighting apparatus, comprising: at least onelight emitting diode (LED) chip configured to emit blue light; a greenphosphor having an emission peak in a range of 500 nm to 550 nm; and ared phosphor having an emission peak in a range of 600 nm to 650 nm,wherein the red phosphor comprises: a first red phosphor having anemission peak in a range of 620 nm to 630 nm; and a second red phosphorhaving an emission peak in a range of 630 nm to 640 nm, wherein thefirst red phosphor and the second red phosphor comprise (Ca,Sr)S:Eu-based phosphors and full widths at half maximum of the first redphosphor and the second red phosphor are in a range of 20 nm to 60 nm,respectively, wherein, in an emission spectrum, an intensity of lightemitted from the lighting apparatus is configured to gradually increasefrom 500 nm to 600 nm, and wherein the intensity of light emitted fromthe lighting apparatus at 700 nm is configured to be less than about 10%of the maximum intensity of light emitted from the lighting apparatus.2. The lighting apparatus of claim 1, wherein a general color renderingindex (Ra) of the lighting apparatus is in a range of 80 to 98, and anR8 thereof is greater than
 72. 3. The lighting apparatus of claim 1,wherein full widths at half maximum of the first red phosphor and thesecond red phosphor are in a range of 50 nm to 60 nm.
 4. The lightingapparatus of claim 1, wherein the green phosphor includes a Lu₃ (Al,Ga)₅O₁₂:Ce (LuAG)-based phosphor.
 5. The lighting apparatus of claim 1,further comprising: a yellow phosphor having an emission peak in a rangeof 550 nm to 600 nm.
 6. The lighting apparatus of claim 1, wherein thelighting apparatus is an LED lamp including an LED filament.
 7. Thelighting apparatus of claim 6, wherein: the LED filament comprises: asupporting substrate on which the LED chips are disposed; wireselectrically connecting the LED chips; and an encapsulant covering theLED chips; and the green phosphor and red phosphor are distributed inthe encapsulant.
 8. The lighting apparatus of claim 7, wherein theencapsulant surrounds the supporting substrate.
 9. The lightingapparatus of claim 1, wherein the maximum intensity of light emittedfrom the lighting apparatus is configured to be in a range of 600 nm to650 nm.
 10. An LED filament, comprising: a supporting substrate; aplurality of light emitting diode chips disposed on the supportingsubstrate, and configured to emit blue light; and an encapsulantcovering the plurality of light emitting diode chips and havingphosphors distributed therein, wherein the phosphors comprise: a greenphosphor having an emission peak in a range of 500 nm to 550 nm; and ared phosphor having an emission peak in a range of 600 nm to 650 nm,wherein the red phosphor comprises: a first red phosphor having anemission peak in a range of 620 nm to 630 nm; and a second red phosphorhaving an emission peak in a range of 630 nm to 640 nm, wherein thefirst red phosphor and the second red phosphor comprise (Ca,Sr)S:Eu-based phosphors and full widths at half maximum of the first redphosphor and the second red phosphor are in a range of 20 nm to 60 nm,respectively, wherein, in an emission spectrum, an intensity of lightemitted from the LED filament is configured to gradually increase from500 nm to 600 nm, and wherein the intensity of light emitted from theLED filament at 700 nm is configured to be less than about 10% of themaximum intensity of light emitted from the lighting apparatus.
 11. TheLED filament of claim 10, wherein a general color rendering index (Ra)of the LED filament is in a range of 80 to 98, and an R8 thereof isgreater than
 72. 12. The LED filament of claim 10, wherein full widthsat half maximum of the first red phosphor and the second red phosphorare in a range of 50 nm to 60 nm.
 13. The LED filament of claim 10,wherein the maximum intensity of light emitted from the LED filament isconfigured to be in a range of 600 nm to 650 nm.